Electronic fuel metering apparatus for internal combustion engine

ABSTRACT

Electronic fuel metering apparatus is described for use with an internal combustion engine having an air inlet passage for supplying air to one or more combustion chambers. The apparatus includes an electrically controlled fuel metering device, a circuit for accumulating a count of air entering the combustion chamber (s), and a circuit for controlling, in accordance with the air count, the amount of fuel discharged by the fuel metering device. An up/down counter may be employed, and the rate at which fuel is discharged may be varied depending upon the air count accumulated on the up/down counter.

United States Patent [191 Brittain et a1.

ELECTRONIC FUEL METERING APPARATUS FOR INTERNAL COMBUSTION ENGINEInventors: William J. Brittain,

Westcliff-omSea; Thomas J. L. Dobedoe, Wateringbury; Raymond Mitchell,Chelmsford; Wilfred T. Oliver, Rugby, all of England Ford Motor Company,Dearborn, Mich.

Filed: Nov. 3, 1972 Appl. No.: 303,661

Assignee:

Foreign Application Priority Data Feb. 3, 1972 Great Britain 5056/72 US.Cl.. 123/32 EA, 123/139 AW, 123/139 E, 123/140 MC Int. Cl F02m 51/00Field of Search. 123/139 E, 139 AW, 140 MC, 123/119 R, 32 EA ReferencesCited UNITED STATES PATENTS 4/1971 Steiger 123/139 E [45 Aug. 27, 19743,682,152 8/1972 Muller-Berner 123/140 MC 3,696,303 10/1972 Hartig123/143 E 3,747,577 7/1973 Mauch et 81. 123/139 AW FOREIGN PATENTS ORAPPLICATIONS 2,004,269 8/1970 Germany 123/32 EA PrimaryExaminer-Laurence M. Goodridge Attorney, Agent, or Firm-Keith L.Zerschling; Robert W. Brown [57] ABSTRACT Electronic fuel meteringapparatus is described for use with an internal combustion engine havingan air inlet passage for. supplying air to one or more combustionchambers. The apparatus includes an electrically controlled fuelmetering device, a circuit for accumulating a count of air entering thecombustion chamber (s), and a circuit for controlling, in accordancewith the air count, the amount of fuel discharged by the fuel meteringdevice. An up/down counter may be employed, and the rate at which fuelis discharged may be varied depending upon the air count accumulated onthe up/down counter.

1 Claim, 5 Drawing Figures Pmmanw z n mmurg FIGJ.

PAIENTEIJ mszmn mama" PAIamsnwsziwn mung m orm ELECTRONIC FUEL METERINGAPPARATUS FOR INTERNAL COMBUSTION ENGINE DESCRIPTION OF THE INVENTIONThis invention relates to an Otto cycle internal combustion engine andto fuel metering apparatus for it.

According to the invention, such an engine has the following features:

a. An electronic logic circuit is responsive to sensing means disposedin an inlet passage to produce electrical signals representative of themass of air flowing through the passage into a cylinder of the engine;

b. the logic circuit controls the mass of fuel injected at a locationdownstream of the sensing means in accordance with said air mass flowsignals Preferably the mass of fuel injected during each inductionstroke of the cylinder is in a predetermined constant ratio to the massof air entering the cylinder during the induction cycle as indicated bysaid air mass flow signals.

1n the embodiment described below the fuel is injected directly into thecylinder but the injector may alternatively be located in the inletmanifold downstream of the air flow sensors.

The invention will now be described with reference to the accompanyingdrawings, in which:

FIG. 1 is a section of one cylinder of a multicylinder Otto cycleinternal combustion engine embodying the invention;

FIG. 2 is a circuit diagram of the injection control system of theengine of HQ 1;

F 1G. 3 is a graph illustrating the'variation of the differentparameters affecting the mass of air entering the cylinder over onecycle of the engine; and

FIGS. 4 and 5 are graphs showing injection timing in relation to airmass in a cylinder.

A multi-cylinder Otto cycle internal combustion engine includes analuminum alloy integral cylinder block and cylinder head 10. A piston 11in each cylinder 12 is connected by a connecting rod 13 to a crankshaft(not shown). In each cylinder, an inlet valve 14 and an exhaust valve(behind the inlet valve in FIG. 1) are actuated by a single overheadcamshaft driven by the crankshaft. i

A spark plug is mounted in spark plug bore 27. The timing of the valveopenings and ignition follows conventional practice in modern Otto cycleengines.

The inlet valve 14 of each cylinder is mounted in a passage 15 whichconnects to an inlet manifold 16 common to all cylinders. A watercarburetor 17 is mounted on to the manifold 16 and a conventional aircleaner (not shown) is mounted on the water carburetor. The watercarburetor is arranged to humidify the air passing through it to theengine to a substantially constant value, for example 100 percentrelative humidity.

A butterfly valve 18 in the water carburetor is connected to a throttlecontrol pedal and regulates the air flow to the engine in accordancewith throttle pedal movement.

A low pressure fuel injector I9 is located in the wall of each cylinder12. The exact location of the injector is chosen having regard to a needfor a reasonably low (e.g., less than I 100C) and reasonably uniformtemperature of fuel passing through the injector to prevent prematurefuel vaporization and to facilitate measurement of the mass of fuelpassing through the injector.

The water jacket 9 of the block 10 completely surrounds the injector foreffective injector cooling. The injector is preferably mounted as low aspossible in the cylinder wall consistant with being uncovered by thepiston for a sufficiently long period during inlet valve opening topermit substantially all fuel to be injected when the inlet valve isopen. This is to permit use of low pressure injectors and to allowfuel/air mixing during the compression stroke.

The fuel injectors may be conventional solenoid operated low pressureinjectors as used in many existing injection systems which inject fuelinto the inlet passage of the cylinder. The valve should however, openoutwards in view of the high pressure which the injector will have towithstand during combustion cycles.

The fuel injectors 19 are connected to a fuel system in which a constantpressure of the order of psi. is maintained by a fuel pump.

The soleoids of the fuel injectors are energized by an electronic logiccircuit. The circuit of FIG. 2 shows the logic associated with onecylinder. Identical independent circuits may be used for the othercylinders but preferably at least part of the circuit is time-sharedwith the other cylinders as described later in this specification.

The inputs to the circuit are provided by sensors or transducers 20through 26. which are responsive, respectively, to air velocity in theintake passage 15, air pressure in the intake passage, air temperaturein the intake passage, humidity, crankshaft position, fuel velocity andfuel temperature.

The sensors for air velocity and pressure are mounted closely adjacentto each other in the inlet passage 15. Temperature and humidity sensors.may be mounted at other locations in the inlet tract and shared with theother cylinders since temperature and humidity will not varysignificantly within a particular engine cycle.

The fuel velocity and temperature sensors may be mounted either in thefuel injector 119 or in the fuel supply line connected to the injector.

The crankshaft position transducer 24 may be an electro-magnetic devicecoupled to the engine flywheels. It produces a signal at the point inthe cycle when fuel injection may begin, i.e.,. the point in theinduction stroke when the piston uncovers the injector. Signals from thecrankshaft position sensor may also control an electronic ignitionsystem.

The measurement of air velocity and fuel velocity accurately and at highspeed is essential for the system to operate effectively. One example ofa flow meter which could be used is described in our British Patent No.1,127,568. Alternatively hot-wire or hot-film anemometers may be used.Such devices are described in the following references:

1. Hot-Wire Anemometers. The Review Of Scientific Instruments, May 1967page (677).

2. P. O. A. L. Davies, M. R. Davis and l. Wold, Open ation of theConstant Resistance Hot-Wire Anemometers Institute of Sound AndVibration University of Southampton, Report No. 189;

3. J. C. Wyngaard and J. L. Lumley, A Constant Temperature Hot-WireAnemometer, Journal of Scientific Instruments, Vol. 44, 1967, page(363);

4. B. J. Bellhouse and D. L. Schultz, The Determination of FluctuatingVelocity in Air with Heated Thin Film Gauges. Journal f Fluid Mechanics,Vol. 2, part 2, 1967 page (289).

The variation of the different parameters effecting the mass of airentering the cylinders during the induction stroke is illustrateddiagrammatically in FIG. 3.

The mass rate of flow of air into the cylinder is a function of the airflow velocity, air temperature, air pressure and humidity, through aknown area. This function is generated by an air mass flow functiongenerator 28, the output signal of which is representative of the rateof mass flow of air into the cylinder. The function generator isconnected to a voltage to frequency converter 29. An up and downcounting register 30 has an up counting input 31 connected to thevoltage to frequency converter 29 so that the register accumulates acount representative of the mass of air which has entered the cylinder.

Gate circuits 32 to 34 each connect a respective stage of the register30 to a pulse generator 35. A signal from the first gate 32 causes thepulse generator to generate pulses with a relatively low mark/spaceratio. A signal from the second gate 33 produces an intermediatemark/space ratio and a signal from the third gate 34 produces an eithera high mark/space ratio or a continuous signal (i.e., infinitemark/space ratio). The output of the pulse generator is applied to anamplifier 36 connected to the solenoid 37 of the fuel injector 19.

The amplifier 36 has sufficient gain that the amplitude of the pulseswhich it produces is sufficient to fully open the fuel injector.However, the frequency of the pulses is greater than the fuel valve canfollow so that the mark/space ratio of the pulse generator determinesthe position assumed by the fuel injector and hence the three availablemark/space ratios provide three rates of flow through the valve.

The actual fuel flow (mass flow) is represented by the output signal ofa fuel flow function generator 38, responsive to fuel velocity and fueltemperatures. The output signal of function generator 38 is converted toa frequency modulated signal in a voltage to frequency converter 39 andapplied to a down counting input 40 of the register 30.

The circuit is such that the frequency at input 31 for a given rate ofair mass flow is in a predetermined ratio to the frequency at input 40for the same rate of mass flow of fuel. This predetermined ratio is thesame as the fuel/air ratio produced by the system. A lean air/fuel ratioof the order of :1 is used in order to minimize harmful exhaustemissions (i.e., unburnt hydrocarbons and carbon monoxide, and oxides ofnitrogen).

Thus, for a 20:1 air/fuel. a certain mass of fuel passing into thecylinder causes a count down 20 times greater than the count up producedwhen the same mass of air flows into the engine.

At any point in the cycle, the register thus stores a countrepresentative of the mass of air in the cylinder for which fuel has notyet been injected in the required air/fuel ratio.

Gates 32 to 34 are opened and closed by a bistable circuit 41. Thecrankshaft position sensing circuit turns on the bistable circuitthrough a monostable circuit 42 at the point in the engine cycle whenfuel injection may begin. The bistable circuit 41 then opens the gates32 to 34.

A level detection circuit 43 is connected to the output of air mass flowfunction generator 28 and produces an output signal when the air massfalls below a 4 predetermined level indicative of the closing of theinlet valve. A time delay circuit 44 responsive to the level detectorcircuit 43 turns off the bistable circuit 41 thereby closing the gates32 to 34 after a short time delay. This time delay is long enough toensure that the inlet valve is fully closed before injection stops butshort enough to avoid the system attempting to inject fuel afterpressure in the cylinder has begun to rise due to the compression strokeof the piston or when the piston covers the injector.

It is an important feature of the engine that injection is complete atthe beginning of the compression stroke because the system relies on thecompression stroke to properly mix the air and fuel in the cylinder.

The time delay circuit 44 also activates a monostable circuit 45 at thecompletion of air induction and fuel injection. The monostable circuit45 resets the register 30 to zero ready for the next cycle.

The operation of the circuit is illustrated in FIGS. 4 and 5. At thebeginning of the induction stroke of the piston, air begins to flow intothe cylinder and the register 30 accumulates a count representative ofthe air mass in the cylinder. Fuel injection does not start immediatelybut is delayed until the injector is uncovered by the piston. At thistime gates 32 to 34 are opened by the crankshaft piston sensor 24. Inlow power operation (FIG. 4) when the butterfly valve 18 is onlypartially open, the count which has accumulated by the time the gates 32to 34 are opened will be of intermediate value, sufficient to turn ongate 33, thereby producing an intermediate value 48 of fuel flow. Thisintermediate value of fuel flow continues until a sufficient number offuel flow units have been counted out of the register to reduce thecount to a level at which only gate 32 is on. Fuel is then injected at alow rate 46.

In high power operation (FIG. 5) the count in the register at thebeginning of fuel injection is sufficient to produce a high rate 47 offuel flow through gate 34. The fuel flow reduces through intermediaterate 48 to low level rate 46 as the fuel injection catches up with theair induction and the count in register 30 decreases.

The correct functioning of the circuit described above depends upon thespeed with which the various operations can be performed. At maximumr.p.m. of the engine, the duration of the induction cycle is about 2milliseconds. If this system does not operate sufficiently quickly therewill be a significant count left in the register 30 at the point whenfuel injection ceases, representing excess air in the cylinder therebymaking the mixture weaker than the design value.

One way of overcoming this problem is to measure the air injected in onecycle and inject a corresponding measured quantity of fuel into the nextcycle. The difference between the successive cycles may not besufficient to upset the desired air/fuel ratio. Such a system couldoperate in an in-cycle mode (i.e., injecting the measured fuel into thesame cycle as the air measurement takes place) at low r.p.m. where theoperation is slower but cycle to cycle variation is greater and switchto following cycle mode as the speed of the engine r1ses.

An alternative type of system attempts to anticipate or extrapolate fromthe first part of the induction cycle what the total air mass will be atthe end of the cycle and to inject fuel in accordance with such acomputed value.

A simple modification to the circuit of FIG. 2 uses the count remainingin the register at the end of the cycle to compensate the next cycle andthereby maintain the design mixture strength at high rpm. The monostablecircuit 45 is omitted so that the register is not reset to zero at theend of the induction cycle. Thus, any count which remains in theregister is added into the next cycle and fuel injection begins athigher rate or remains at the higher rate for a longer period. At theend of this next cycle, the register will still hold a residue, whichwill be approximately equal to the residue at the end of the previouscycle so that the correct mass of fuel will have been injected. As thespeed of the engine increases, the residue in the register 31 at the endof each cycle becomes greater as the operation effectively changes fromin-cycle mode to following cycle mode.

The whole of the circuit of FIG. 2 may be provided for each cylinder butconsiderable economies of circuitry can be achieved by time-sharing atleast part of the circuit between the different cylinders. This ispossible because the induction cycles take place sequentially. In a fourcylinder engine, for example, two logic circuits each time sharedbetween two cylinders would be adequate,

All of the circuit of FIG. 2 except the air flow sensor,

the air pressure sensor, the fuel velocity sensor and the injectionsolenoid can be time shared in this way.

If the modified circuit omitting monostable 45 is used, separateregisters 30 for each cylinder may be necessary.

We claim:

1. Electronic fuel metering apparatus for an internal combustion enginehaving an air inlet passage for supplying air to at least one combustionchamber in said engine, said apparatus comprising: an electronicallycontrolled fuel metering device; first circuit means for accumulating acount of air entering said engine combustion chamber; second circuitmeans, connected to said electrically controlled fuel metering device,for controlling the amount of fuel metered therefrom in accordance withthe air count accumulated on said first circuit means; said first andsecond circuit means being interconnected and including means forreducing said accumulated air count by an amount determined by theamount of fuel metered by said fuel metering device, said first andsecond circuit means further including means for varying the rate atwhich fuel is discharged from said fuel metering device, said rate beingreduced in steps as said air count is reduced by said means for reducingsaid accumulated air count.

1. Electronic fuel metering apparatus for an internal combustion enginehaving an air inlet passage for supplying air to at least one combustionchamber in said engine, said apparatus comprising: an electronicallycontrolled fuel metering device; first circuit means for accumulating acount of air entering said engine combustion chamber; second circuitmeans, connected to said electrically controlled fuel metering device,for controlling the amount of fuel metered therefrom in accordance withthe air count accumulated on said first circuit means; said first andsecond circuit means being interconnected and including means forreducing said accumulated air count by an amount determined by theamount of fuel metered by said fuel metering device, said first andsecond circuit means further including means for varying the rate atwhich fuel is discharged from said fuel metering device, said rate beingreduced in steps as said air count is reduced by said means for reducingsaid accumulated air count.